Rotatable anode x-ray tube



Jan. 2, 1940. 2. J. ATLEE 2,185,825

ROTATABLE ANODE X-RAY TUBE Filed June 7, 1938 Inventor: Zed J. Atlee 0SPEED SYNCHRONOUS by W 7 SPEED Hi8 Attorney I Patented Jan. 2, 1940PATENT OFFICE ROTATABLE ANODE X-RAY TUBE Zed J. Atlee, Chicago, Ill.,assignor to General Electric X-Ray Corporation, a. corporation of NewYork Application June 7, 1938, Serial No. 212,268

4 Claims.

The present invention relates in improvements in X-ray apparatus of thetype which includes an X-ray tube having a stationary electrode and arelatively rotatable electrode.

It is an advantage of X-ray tubes of this character that they are ableto operate with very high discharge currents. However, the safe use ofsuch currents depends upon the maintenance of a definite speed ofrotation of the relatively movable electrode. To employ the fulloperating current with the movable electrode stationary or rotating atreduced speed may result in serious damage to the X-ray target.

It is an object of my present invention to provide means forautomatically preventing the supply of normal discharge current to arotating element X-ray tube unless and until the said element isrevolving at its intended speed.

The features of novelty which I desire to protect herein are pointed outwith particularity in the appended claims. The invention itself togetherwith further objects and advantages thereof may best be understood byreference to the following description taken in connection with thedrawing in which Fig. 1 illustrates diagrammatically an X-ray apparatussuitably embodying the invention and Fig. 2 is a graphicalrepresentation useful in explaining the invention.

Referring particularly to Fig. 1, I have shown an Xray tube of the typedescribed in application Serial No. 78,996, filed May 11, 1936, in thenames of Malvern J. Gross and Zed J. Atlee. This comprises a sealedevacuated envelope Ill enclosing a separately heated cathode, shown inoutline at It, and a rotatable anode I2 having thereon an inclinedperipheral target face 3. The anode it is intended to be rotated duringnormal operation and is mechanically connected to a driving meanscomprising an induction rotor 54. The rotor may comprise a squirrel cageconstruction such as is described and claimed in the application SerialNo. 78,996 above referred to. In order to supply driving force to therotor it there provided an electromagnetic stator which is outside thedischarge envelope and which is indicated diagrammatically in dottedoutline at E5. The stator is provided with polyphase windings l6 and ll(shown separately of the stator for clarity) whose character and mode ofenergization will be set forth more fully hereinafter.

The energizing means for the various instrumentalities is shown ascomprising a common power source I8 which is connected to anautotransformer I9 through a manually operable switch 2i. 'Theauto-transformer is provided with a plurality of terminals which make itpossible to derive a number of different potentials from the samevoltage source.

One set of these terminals, namely, terminals 23 and 24, are used forsupplying heating current to the cathode I! through the intermediationof a transformer 25. Regulation of the heating current is accomplishedby means of a variable resistor 26 connected in series with thetransformer primary.

The main discharge current for the X-ray tube is provided by means of atransformer 21 which has its primary connected between terminals 23 and28 of the auto-transf0rmer 19. The energizing cir uit thus provided iscontrolled jointly by a manually operable switch 29 and by a sole-- noidoperated relay 30, the operation of which will be more fully explainedhereinafter.

Referring again to the windings I6 and I! of the stator I5, it should bepointed out that these are of such character as to provide a rotatingmagnetic field when supplied with polyphase currents. In order to obtainsuch currents from the single phase source 3, a phase-splitting deviceis employed in the form of a condenser 32. In operation, the potentialwhich exists between terminals 23 and 35 of the auto-transformer i9 isapplied directly to the stator winding I6 by means of conductors 36 and31. It is applied indirectly to the winding ll through these sameconductors connected in series with the condenser 32. The action of thiscondenser is to produce a phase difference between the currents flowingin the two windings so as to obtain the effect of polyphase excitationof the stator. By this means a rotating magnetic field is produced whichis effective to exert a strong torque on the rotor I 4 and to rotate itand the connected anode'l2.

Rotation of the anode I2 during use causes the heating efiect of thedischarge current passing between it and the cathode II to bedistributed over the entire target surface I3 and obviates the danger oflocalised burning. The amount or" discharge current which can be safelyhandled is a function of the speed of rotation and may be very highunder proper conditions. However, the use of extremely high currentsinvolves the danger that a decrease in speed below the intended valuemay result in destructive hearings on which the rotating parts aresupported.

In accordance with my present invention, means is provided for assuringthat the discharge circuit shall be fully energized only when the rotorI4 is turning at its normal speed or at a speed not materially belownormal. To this end there is provided in connection with the statorenergizing circuit, means effective to control the operation of therelay 30 in such a manner as to accomplish the desired result. Thismeans comprises a device which is responsive to an electrical conditionof the stator energizing circuit, specifically a solenoid operated relay39 which is controlled by variations in voltage across the statorwinding IT. The particular control arrangement shown includes acondenser 4| and a pair of resistors 42 and 43 connected in seriesacross the stator winding I1. coil .of the relay 39 is connected acrossthe condenser so that the relay is maintained in its closed positionwhen and as long as the voltage of the condenser 4| is in excess of apredeter- -mined minimum value.

It will be observed that actuation of the relay opens the upper contacts48, 49 of the relay and places the resistor 42 in circuit with thewinding H. This'makes the relay more sensitive to a slight drop involtage. The condenser 4i has the eiTect of preventing chattering actionof the relay.

The action of the control circuit just described may be understood byreferring to Fig. 2 which shows the relationship which exists betweenthe time, the speed of the rotor again drops, say, tov

the point B, the relay 39 will reopen.

Closure of the relay 39'serves to complete the energizing circuit forthe relay 30--at least insofar as this circuit depends upon theexistence of a connection between relay terminals 46 and 4?. (There1ay30 is under the joint control of the relay 3i) and of anexposure-timing device 50). The complete relay circuit may be tracedfrom terminal 5! of the auto-transformer I9 through the coil of relay30, timer 50, conductor 52, relay contacts 46 and 41, and conductor 53back to terminal 23 of the auto-transformer.

Assuming that the timer 5!! is in its closed position, closure of therelay 39 will permit the supply of discharge current to the X-ray tube.Furthermore, subject to the operation of the timer 50, such dischargecurrent may be continued as long as the speed of the rotor l4 remainsabove the predetermined minimum. If, for any reason this speed dropsbelow such minimum, the relay 39 will open so as to prevent further flowof discharge current and consequent damage to the Xray target. Theoperation of the relay 39 may be adjusted to provide for its closure atdifferent speeds of the rotor. [4 or its use at difierent voltages byvarying thefvalues of the resistors 42 and 43. It will be understoodthat as the value of the resistors is decreased the proportion of thetotal voltage'which appears across the condenser The energizing- 4| willincrease. Consequently the relay will remain closed for lower speedsthan would be the case with higher resistor values.

It is not necessary that the relay 39 operate to interrupt the supply ofdischarge current completely. It would be a sufiicient protection, forexample, if its operation were to introduce into the discharge circuitan impedance of such magnitude as to reduce the current flow to a safevalue.

It will further be understood that the particular circuit which I haveillustrated is in no Way essential to the purposes of the invention.Various changes may be made by those skilled in the art and I aim in theapp-ended claims to cover all such equivalent modifications as fallwithin the true spirit of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an apparatus of the type which includes a discharge tube having astationary'electrode, a rotatable electrode and electromagnetic meansfor driving the rotatable electrode, the combination which comprises afirst electrical circuit for supplying operating current to the saidtube, a second electrical circuit for energizing the said electrodedriving means, the electrical conditions of said second circuit beingvariable in accordance with variations in the speed of rotation of saidelectrode, and means associated with said second circuit and responsiveto an electrical condition thereof for preventing the supply of normaloperating current to the tube except upon the attainment of a desiredspeed of rotation of the said rotatable electrode.

2.-In an apparatus of the type which includes an 'X ray tube having astationary cathode, a rotatable anode, an electromagnetic rotormechanically connected to the anode and an electromagnetic stator forsupplying driving force to'the rotor, the combination which comprises afirst electrical circuit for supplying discharge current to the tube, asecond electrical circuit for supplying energizing current to thestator, the electrical conditions of said second circuit being variablein accordance with variations in the speed of rotation of said rotor,and means associated with said second circuit and responsive to anelectrical condition thereof for preventing the completion of the saiddischarge current circuit except upon the attainment of I a desiredspeed of rotation of the rotor.

3. In an apparatus of the type which includes an X-ray tube having acathode, a rotatable anode, an electromagnetic rotor mechanicallyconnected to the anode, and an electromagnetic stator for supplyingdriving force to the rotor, the combination which comprises a firstelectrical circuit for supplying discharge current to the tube, a secondelectrical circuit including energizing windings for the stator, atleast certain of said windings being of such character that the voltagedrop therethrough varies materially in response to variations in thespeed of rotation of the rotor and means responsive to such variationsin voltage drop for preventing completion of the said first circuitexcept upon the existence of a predetermined speed of rotation of therotor.

4. An X-ray apparatus including an X-ray tube having a stationarycathode and a rotatable anode, an electrical circuit for supplyingdischarge current to the tube, an induction rotor connected with theanode for driving the same, an electromagnetic stator having a pair ofpolyphase windings "for supplying driving force to the rotor, a 75source of single phase potential adapted to be connected directly to oneof said windings and indirectly to the second winding through a phaseshifting device, a relay for controlling the said discharge currentcircuit, and means responsive to the potential drop across the saidsecond stator winding for controlling the operation of the relay,whereby the supply of normal discharge current to the tube is madedependent on the attainment of a desired operating condition of therotor.

ZED J. ATLEE.

